Bad reflections on some faces in blender, good on substance painter
The problems were caused by some non-planar quads as lemon said in the comments. For some reason, the direction in which tris are generated on those specific quads is important. Maybe in the bake, they were autogenerated in the opposite direction. I think that's the case, because when I join vertices to make edges in the opposite direction of the shading, all is fixed.
The topology could be better and include some edge loops on the sides, so the non-planar quads don't even exists at all, but well, for the moment, it works!
Some pictures to improve understanding of this kinda problem. This is the model in solid and render pre-fix:
 
And this is post-fix:
 
After that, I just re-baked the lowpoly, and worked like a charm. Thanks, everyone!